Unable to perform assignment because the left and right sides have a different number of elements.

I am trying to calculate all values of velocity and displacement for the times between 0 and 20 in increments of 0.01. Im struggling to add on the last value of velocity and displacement as i need to be able to use the previous iteration values where i have tried doing this using the variable 'i'. I think the problem is due to the different sizes of matrices. Im quite new to coding so any help would be appreciated, thanks.

[Katie]

Can you please attach or copy your code so we can see how you're setting it up? Thanks!

Answer 1

[Walter Roberson]

dt = 0.01;
i0 = 1;
i(1) = i0;
i = (1:dt:21);

Note that overwrites all of i

It is not recommended to use i as a variable name, as it can lead to confusion because i is used as sqrt(-1)

i will be a vector of length 2001 I think.

for t = [0:0.01:20.0]
   v(i+1) = a*0.01 + a(i)*t;

You ask to index a(i) but a appears to be a scalar at that point, and i contains non-integer values that are not valid as indices.

You also multiply all of a by 0.01 so if a is a non-scalar (due to code you did not show us) then it might not be the same size as a(i) .

If somehow (that is, if the code you posted is not the code that generated the error) i were a scalar integer at that point but a were a vector, then v(i+1) would hypothetically designate a scalar, but a*0.01 would be a vector and you would be trying to store a vector result into a scalar field.

... But the code you posted would have failed before that, failing when trying to index a at the non-integer i

[Robin Oldfield]

Have you any idea on what I should now do to resolve this? Im very much a novice at coding so Im not sure how i woul change all of these variables into vectors which is what Im assuming i need to do

[Walter Roberson]

I suggest you read https://www.mathworks.com/matlabcentral/answers/395816-why-do-i-get-array-indices-must-be-positive-integers-or-logical-values-error-when-using-angle-fu#comment_882605

[Robin Oldfield]

very helpful thank you very much!